Articles of apparel and fabrics made using spandex knitted fabrics (developed and sold by duPont under the name LYCRA(trademark)) have long been popular because of their close fit, expandability, and comfort. Spandex is an elastomeric man-made fiber having elastic qualities generally considered superior to those of rubber, which it has largely replaced. In many such fabrics spandex is used along with other natural or man made fibers to create a fabric that is not only stretchable, but may also have the desirable characteristics of wrinkle-resistance and washability.
An elastic yarn may consist solely of a number of elastomeric fibers combined to make a xe2x80x9cbarexe2x80x9d elastomeric yarn, such as spandex, or the yarn may use the elastic strand as a monofilament core in a composite yarn having inelastic staple fibers as an outer covering. A yarn such as this is said to be xe2x80x9ccore spun.xe2x80x9d A number of advantages have been found to using core spun elastomeric yarn in fabrics. Among these advantages are appearance, improved handling characteristics, shrinkage control, protection of the core against perspiration and grease, color fastness, control over elongation, and greater power of recovery. Some of these benefits are noted by Humphreys in U.S. Pat. No. 3,017,740. In addition, the outer covering, which may be composed of natural fibers such as cotton, manmade fibers such as polyester, or a combination of both, provides additional breathability to fabrics in which it is used, as contrasted with fabrics made using a bare elastomeric yarn.
Although knitted fabric using bare spandex has recently been introduced into the market for bed sheets, and particularly bed sheets for use in hospitals and other health care facilities, knitted bed sheets and other coverings using core spun elastomeric yarns have not previously been used. The use of bare spandex in the hospital sheet environment is described in U.S. Pat. No. 6,164,092 to Menaker, who notes that a stretchable bed sheet enjoys a number of benefits, including easier installation on a mattress, resilience during repeated washings, and resistance to xe2x80x9cbrunching upxe2x80x9d under a patient. Menaker describes a knitted bed sheet in which the elastomeric yarn will have a 1-to-1 ratio with poly-cotton yarn, and will constitute between 0.01% and 10% of the weight of the finished material. That is, even though the substantial weight of the finished sheet will be accounted for by non-elastic natural or man made fibers, there will be one strand of elastomeric yarn for each strand of non-elastic yarn used in the fabric.
While Menaker""s use of bare spandex in bed sheets signifies an improvement over the prior art, there are some drawbacks associated with the use of bare spandex in such fabrics. For example, bare spandex is knitted under tension so that the fabric will naturally assume a desired shape when it is relaxed. This places the bare spandex yarn under modest tension even when the fabric is not being stretched. As a result of this modest tension, if a spandex yarn should break, the broken ends will pull away from the break, causing localized fraying and resulting in the two loose ends obtruding from the fabric. In a hospital or health care setting, the common use of safety pins, clips, and other fasteners to hold tubes, bed adjustment controls, and television remote control units in proximity to a patient may make holes in a bed sheet that exacerbates the breakage problem which then becomes further exacerbated by the frequent washings to which hospital sheets are subjected. Another drawback to Menaker""s knitted bed sheet is its relative lack of breathability when applied in a snug fit over a liquid and air impermeable hospital mattress cover or other non-breathable surface.
Thus, there is a need for a breathable knitted fabric for use in covering impermeable materials such as hospital mattresses and that will not exhibit fraying or obtruding strand ends when yarn breakage occurs through normal usage of the article.
This invention uses a core spun elastomeric yarn to overcome the problems encountered with a bare elastomeric yarn. A core spun elastomeric yarn provides protection for an elastomeric core within the outer covering and will tend to keep the elastomeric core from breaking, should a sharp implement penetrate the fabric. Even if the elastomeric filament in the core should become broken, the outer covering will hold the two broken ends in proximity to one another, and will prevent them from withdrawing from the site of the break. By maintaining the integrity of the yarn and the fabric, the core spun elastomeric yarn will prevent the fraying at the point of breakage that is found to occur with a bare elastomeric yarn.
In addition, a core spun elastomeric yarn can be knitted into a fabric so as to present a smooth surface on one side and a ridged, or ottoman effect on the opposite side. This may be done by adjusting the ratio of ends of core spun elastomeric yarn to ends of inelastic yarn and by adjusting the sizes of the respective yarns. When a smaller size inelastic yarn is used with a large size core spun elastomeric yarn in a 3:1 ratio, a fabric that is smooth on one side and ridged on the other is produced. If the ridged side is placed next to an impermeable surface, the ridges act as pillars to hold the fabric away from the impermeable surface and promote airflow beneath and through the knitted fabric.
Color permeation is also improved with a core spun elastomeric yarn. Because a bare elastomeric yarn may not hold color well, prints and other colored knit fabrics using a bare elastomeric yarn may show minute white spots or discolorations in which the bare elastomeric yarn is visible and has not taken on the same color as surrounding fibers. However, a core spun elastomeric yarn will not exhibit this flaw since the outer covering is made of a staple fiber that will hold whatever color was imparted into the surrounding fibers.
The outer covering of a core spun elastomeric yarn may also provide control for the elasticity and power of recovery of fabrics made from core spun elastomeric yarn. When the yarn is stretched, the outer covering may reach the limit of its extension before the elastomeric monofilament has reached its extreme limit. Such a fabric will reach its maximum stretch length upon the application of modest tension while still maintaining its full power of recovery. These and other benefits of a fabric using a core spun elastomeric yarn will be more fully explained in the following description of the invention.